(1) Field of the Invention
The present invention relates to a developing unit and an image forming apparatus using this. The present invention is, in particular, directed to a developing unit for visualizing an electrostatic latent image formed on a photoreceptor drum with a developer that has been electrified by blending two components, i.e., an electrostatically chargeable toner and a magnetic carrier, wherein toner which falls from the developing roller's developing area for supplying toner to the photoreceptor drum is collected, as well as to an image forming apparatus using this.
(2) Description of the Prior Art
In a conventional image forming apparatus such as a printer etc. using the electrophotography, a printout of an image is formed by electrifying a photoreceptor drum that is driven rotationally by a charger, forming an electrostatic latent image by illuminating the photoreceptor drum with light in accordance with image information, forming a toner image by applying toner to the electrostatic latent image by a developing unit and transferring the toner image to a sheet material or other recording media.
As a developer used for the developing unit of the image forming apparatus, use has been made of, for example a dual-component developer which is prepared by mixing two components, or an electrostatically chargeable toner and a magnetic carrier.
The thus constructed image forming apparatus entails the problem that the toner scattering from the developing roller of the developing unit adheres onto the photoreceptor drum surface and the thus adhering toner transfers to the recording medium, the transfer belt or the like, degrading image quality.
Further, with increase in the processing speed and with downsizing of the carrier particles (e.g., the carrier's particle size has reduced from 80 μm to 50 μm in diameter) to support high-speed configurations of recent image forming apparatus, another problem has emerged that the carrier drops from the developing roller surface, dirtying the apparatus interior and also producing scratches on the photoreceptor drum with the dropping carrier.
To deal with these conventional problems, there has been a proposal in that a toner collecting roller with a scraper is provided for the developing unit so as to collect scattered toner and the collected developer having adhered on the toner collecting roller is removed by the scraper (see patent document 1: Japanese Patent Application Laid-open Hei 7-319279).
When in the above-described prior art the scraper is mounted to the developing unit, it is a common practice that in order to make the scraper uniformly abut the toner collecting roller, the scraper is backed with a reinforcement arranged on the scraper supporting side and fixed to the scraper fixture etc., using screws at plural places (some or several places).
However, since the scraper becomes worn out at its front contact part which is put in sliding contact with the toner collecting roller, the scraper needs to be replaced periodically upon maintenance. For this reason, the scraper attachment structure with screw fastening as stated above entails the problem that the work in assembling the scraper and its replacement for maintenance are complicated.
Further, the attachment structure of the scraper with screw fastening gives rise to a fear that the scraper might be deformed by stress concentration at the screw-fastened positions and also makes the developing unit bulky.